Exponent

About: Exponent is a company organization based out in Menlo Park, California, United States. It is known for research contribution in the topics: Population & Risk assessment. The organization has 1589 authors who have published 2680 publications receiving 88140 citations.

Validation of a micro-CT technique for measuring volumetric wear in retrieved acetabular liners.

Abstract: In this study, a novel micro-CT–based technique for evaluating wear in retrieved acetabular liners was introduced and validated. Six UHMWPE acetabular components ranging in implantation time from 2.7 to 14.4 years were collected and evaluated with the use of a high-resolution micro-CT scanner. The components were scanned with a uniform volumetric resolution of 74 microns (16-bit precision) with the use of a 1024 × 1024 in-plane image matrix. Manual rigid 3D image registration of the interior hemispherical portion of the acetabular cup with geometric primitives by trained observers allowed for isolation, visualization, and measurement of the wear volume. Results for these six components indicated an average wear rate of 65 mm3/year. Overall scanner error was quantified gravimetrically and associated with a maximum uncertainty of 0.6%. Intra- and interobserver uncertainty analysis showed the method to be both accurate and repeatable. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005

Viscoelastic and failure properties of spine ligament collagen fascicles

Abstract: The microstructural volume fractions, orientations, and interactions among components vary widely for different ligament types. If these variations are understood, however, it is conceivable to develop a general ligament model that is based on microstructural properties. This paper presents a part of a much larger effort needed to develop such a model. Viscoelastic and failure properties of porcine posterior longitudinal ligament (PLL) collagen fascicles were determined. A series of subfailure and failure tests were performed at fast and slow strain rates on isolated collagen fascicles from porcine lumbar spine PLLs. A finite strain quasi-linear viscoelastic model was used to fit the fascicle experimental data. There was a significant strain rate effect in fascicle failure strain (P < 0.05), but not in failure force or failure stress. The corresponding average fast-rate and slow-rate failure strains were 0.098 ± 0.062 and 0.209 ± 0.081. The average failure force for combined fast and slow rates was 2.25 ± 1.17 N. The viscoelastic and failure properties in this paper were used to develop a microstructural ligament failure model that will be published in a subsequent paper.